Abstract
Biocatalysis has developed in the last decades as a major tool for green polymer synthesis. The particular ability of lipases to catalyze the synthesis of novel polymeric materials has been demonstrated for a large range of substrates. In this work, novel functional oligoesters were synthesized from ε-caprolactone and D,L/L-malic acid by a green and sustainable route, using two commercially available immobilized lipases as catalysts. The reactions were carried out at different molar ratios of the comonomers in organic solvents, but the best results were obtained in solvent-free systems. Linear and cyclic oligomeric products with average molecular weights of about 1500 Da were synthesized, and the formed oligoesters were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis. The oligoester synthesis was not enantioselective in the studied reaction conditions. The operational stability of both biocatalysts (Novozyme 435 and GF-CalB-IM) was excellent after reutilization in 13 batch reaction cycles. The thermal properties of the reaction products were investigated by thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis. The presence of polar pendant groups in the structure of these oligomers could widen the possible applications compared to the oligomers of ε-caprolactone or allow the conversion to other functional materials.
Highlights
Albeit large-scale utilization and continuous development of the “classical” catalytic pathway of polymer synthesis still continues, enzyme-catalyzed polymerization has emerged as a valuable approach since the early 1980s, in the case of specialty polymers, leading to green polymer chemistry [3]
99%), 2-methyl-tetrahydrofuran, and lipase B from Candida antarctica immobilized on acrylic resin (Novozyme 435) were Sigma-Aldrich products acquired from Merck KgaA
In the case of the synthesis of malic acid polymers/oligomers with diols, this structural characteristic is not important, the polyester formed with the participation of both carboxyl groups, leaving the hydroxyl group as a pendant
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The synthesis of polymers, which belong to the most important synthetic materials manufactured at the industrial scale, began about 100 years ago, using chemical catalysts. Homogeneous and heterogeneous chemical catalysts, including acids, bases, radicalgenerating compounds, metal-based catalysts, etc., still represent the most important option for efficient and selective polymer production, showing remarkable progress in the last years in the development of controlled radical polymerizations [1] or the utilization of metalorganic framework materials [2]. Albeit large-scale utilization and continuous development of the “classical” catalytic pathway of polymer synthesis still continues, enzyme-catalyzed polymerization has emerged as a valuable approach since the early 1980s, in the case of specialty polymers, leading to green polymer chemistry [3]
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